1. Field of the Invention
The present invention relates to a developing unit, a developing device, an image-forming apparatus, and a computer system.
2. Description of the Related Art
As one type of an image-forming apparatus, there is known an apparatus comprising a plurality of developing devices (which are also called “developing units”) arranged radially about an axis of rotation. The developing devices are capable of developing a latent image formed on a photoconductor using a developer, such as toner. When an image signal is transmitted from an external device such as a host computer, the image-forming apparatus makes the developing device rotate about the axis of rotation in order to locate one of the plurality of developing devices in a developing position opposing the photoconductor. A toner image is created by developing the latent image formed on the photoconductor, and the image is transferred to an intermediate medium. A color image is formed by superimposing the plurality of toner images, by sequentially changing the plurality of developing devices and repeating the above-mentioned developing and transferring processes.
(1) One type of developing device comprises: a container for containing the toner; a developing roller that serves as a developer bearing member and is rotatably supported on the container by a shaft; and a toner supplying roller that is also rotatably supported on the container by a shaft. The toner supplying roller is made from an elastic body and serves as a developer supplying member that can supply toner onto the surface of the developing roller by pressing against it.
Toner must stably be supplied to a “abutting section” (which is also called a nip) where the toner supplying roller elastically abuts against the developing roller. However, in the above-mentioned image-forming apparatus, there are cases in which variations arise in the amount of toner supplied to the abutting section or in pressure applied to the abutting section, due to the difference in the amount of toner remaining in the container. As a result of such a variation, changes may be brought about, for example, in the charging characteristic of the toner supplied to the developing roller, thereby causing reduction in the quality of the formed image.
(2) Another type of developing unit comprises: a container for containing the toner; a developing roller that serves as a developer bearing member and is rotatably supported on the container by a shaft; and a toner supplying roller that is also rotatably supported on the container by a shaft. The toner supplying roller is made from an elastic body and serves as a developer supplying member that can supply toner onto the surface of the developing roller by pressing against it. Further, the developing unit comprises a sealing member for preventing the toner from passing by the circumference of the developing roller and escaping from the container. Further, the developing unit may comprise a thickness-restricting member for restricting the thickness of the toner bore by the developer bearing member. The thickness-restricting member may serve as the sealing member.
In the above-mentioned image-forming apparatus, when the developing unit is made to rotate at high speed in order to allow faster image forming, there is a possibility that the toner will surge at a high pressure upon a section between the developing roller and the sealing member or a section between the developing roller and the thickness-restricting member as if it were colliding against those sections, escape from a gap at the sealing section, and contaminate the image-forming apparatus.
(3) Another type of developing unit comprises: a container for containing the toner; a developing roller that serves as a developer bearing member and is rotatably supported on the container by a shaft; and a toner supplying roller that is also rotatably supported on the container by a shaft. The toner supplying roller is made from an elastic body and serves as a developer supplying member that can supply toner onto the surface of the developing roller by pressing against it.
Toner must stably be supplied to an “abutting section” (which is also called a nip) where the toner supplying roller elastically abuts against the developing roller. However, in the above-mentioned image-forming apparatus, when the developing unit is made to rotate at high speed in order to allow faster image forming, there is a possibility that the toner will flow with great force and surge upon the abutting section at a high pressure as if it were colliding against the abutting section. If the toner is not stably supplied to the abutting section, changes may be brought about in, for example, the charging characteristic of the toner supplied to the developing roller, thereby causing reduction in the quality of the formed image.
(4) Another type of developing device comprises: a container for containing the toner; a developing roller that serves as a developer bearing member and is rotatably supported on the container by a shaft; and a toner supplying roller that is also rotatably supported on the container by a shaft. The toner supplying roller is made from an elastic body and serves as a developer supplying member that can supply toner onto the surface of the developing roller by pressing against it. Further, the developing device comprises a sealing member for preventing the toner from passing by the circumference of the developing roller and escaping from the container. Further, the developing device may comprise a thickness-restricting member for restricting the thickness of the toner bore by the developer bearing member. The thickness-restricting member may serve as the sealing member.
Toner must stably be supplied to a “abutting section” (which is also called a nip) where the toner supplying roller elastically abuts against the developing roller. However, there are cases in which a variation arises in the downward pressure of the toner supplied to the abutting section caused by gravitation, due to the difference in the amount of toner remaining in the container. As a result of such a variation, changes may be brought about in, for example, the charging characteristic of the toner supplied to the developing roller, thereby causing reduction in the quality of the formed image.
Further, due to the difference in the amount of toner remaining in the container, there is a possibility that the toner will surge at a high pressure upon a section where the sealing member abuts against the developing roller or a section where the thickness-restricting member abuts against the developing roller, escape from a gap at the sealing section, and contaminate the image-forming apparatus.
Further, in the above-mentioned image-forming apparatus, when the developing device is made to rotate at high speed in order to allow faster image forming, there is a possibility that the toner will flow with great force and surge upon the abutting section at a high pressure as if it were colliding against the abutting section. This may prevent the toner from being stably supplied to the abutting section. Further, due to the flow caused by rotation, there is a possibility that the toner will surge at a high pressure upon a section between the developing roller and the sealing member or a section between the developing roller and the thickness-restricting member, escape from a gap at the sealing section, and contaminate the image-forming apparatus.
(5) Another type of developing device is shown in FIG. 30. The developing device shown in FIG. 30 comprises a toner container 62 for containing toner 61. In the toner container is provided a toner supplying roller 63 rotatably supported by a shaft. A rotatably-supported developing roller 64 is provided right outside the developing device and abuts against the toner supplying roller 63 through an opening of the developing device. Outside the developing device, the developing roller 64 abuts against a photoconductor 65.
In such a developing device, the toner supplying roller 63 rotates clockwise in FIG. 30, carrying the toner 61 in the toner container 62 to the developing roller 64. The developing roller 64 rotates counterclockwise in FIG. 30, receives the toner at a contacting surface (contacting section) at which it abuts against the toner supplying roller 63, and carries the toner 61 to the photoconductor 65. During this process, some of the toner 61 bore by the developing roller 64 is scraped off by a restriction blade 6, and the amount of the toner 61 is restricted. After development, the toner 61 remaining on the developing roller 64 is stripped off by the toner supplying roller 63.
In the above-mentioned developing device, by setting the circumferential velocity of the toner supplying roller 63, which supplies the toner 61 (developer), larger than that of the developing roller 64, which carries the toner 61, the toner supplying roller 63 will be able to stably supply the toner 61 to the developing roller 64. However, in this case, it becomes necessary to collect the toner 61 that has passed the contacting surface without adhering to the developing roller 64, the toner 61 that has been scraped off by the restriction blade 66 after being supplied to the developing roller 64, and the toner 61 that has been stripped off from the developing roller 64 after development by the toner supplying roller 63. If the toner 61 is not duly removed, the toner 61 will pile up after passing the contacting surface, and as a result, the toner will not be supplied stably to the developing roller 64.
(6) Another type of developing device is shown in FIG. 31. FIG. 31 shows some main structural components of a developing device. The developing device shown in FIG. 31 comprises: a first container 71 and a second container 72 for containing toner T; a developing roller 73 that serves as a developer bearing member and is rotatably supported in the first container 71 by a shaft; and a toner supplying roller 74 that is also rotatably supported in the first container 71 by a shaft. The toner supplying roller 74 is made from an elastic body and serves as a developer supplying member that can supply the toner T onto the surface of the developing roller 73 by pressing against it.
In FIG. 31, a gap that (i) exists on a plane that passes through the center of rotation of the toner supplying roller 74 and forms an angle θ with a horizontal plane, which is taken as a reference and extends from the center of rotation of the toner supplying roller 74 towards the opposite side of the photoconductor 5, in a direction opposite to the rotating direction of the toner supplying roller 74 and (ii) exists between the toner supplying roller 74 and the inner wall of the first container 71 is assumed to be Δd′. In the developing device shown in the figure, Δd′ has a constant value throughout the range of 0°≦θ≦90°, taking the above-mentioned horizontal plane as the reference. The toner T is shoved into a narrow space during the range of 0°≦θ≦90° and pressed by the rotation (clockwise in FIG. 31) of the toner supplying roller 4. As a result, the inner pressure of the toner increases. Then, as the toner T reaches the point of the above-mentioned horizontal plane (θ=0°), its inner pressure is suddenly relaxed. As a result, the toner T bursts forth in a direction perpendicular to the above-mentioned horizontal plane. The toner T having burst forth is carried by the toner supplying roller 74 and flows towards a gap between the developing roller 73 and the container 76.
In such a developing device, if the rotating speed of the developing roller and the toner supplying roller is increased in order to allow faster image forming and/or the flowability of the toner is enhanced in order to ensure suppliability of the toner, the toner will escape from the gap between the developing roller and the container as the developing roller and the toner supplying roller are driven. This may cause contamination of the image-forming apparatus or defective images due the toner adhering to the image-forming section.
(7) Another type of developing device comprises a container for containing the toner, which is a magnetic substance, and a developing roller, which serves as a developer bearing member. The developing roller is rotatably supported on the container by a shaft, and has a magnet inside.
In such an image-forming apparatus, when the developing device is rotated about the axis of rotation, a situation occurs in which a gap between the developing roller and the toner container of the developing device is located beneath the toner. In such a situation, there is a possibility that the toner will escape through the gap by gravitation and contaminate the image-forming apparatus.